Papers by Keyword: Plasma Spray Coating

Abstract: Thermal Barrier Coating are highly advanced material systems usually applied to metallic surfaces, such as gas turbine or aero-engine parts, operating at elevated temperatures. They have ceramic and metallic multilayers which have been widely used in the aeroturbine engines to increase the life of metallic components and turbine efficiency. Many different types of coatings are used to protect variety of engineering materials from wear, corrosion and erosion. Of all these, TBC’s play a vital role in providing thermal insulation and protect the material from high temperature environment. In this paper Lanthanum Zirconate (La₂Zr₂O₇) is used as a coating material which is phase-stable to its melting point, Lanthanum Zirconate is a promising material which exhibit lower thermal conductivity and higher thermal stability compared to other TBC system. High quality Lanthanum Zirconate based TBC is developed by plasma spray technique on superalloys. In the present investigation porosity, microstructure, hardness and bond strength of the developed TBC’s were characterized and significant parameters of plasma spray process were identified.

Abstract: In the present study, a plasma spray coating for titanium particles was studied using software simulations. The governing equations to solve the velocity and temperature distributions of plasma flow and titanium particles considered the effects of electric/magnetic inductions. Seven controlling factors were included in order to investigate their effects on the velocity and temperature of titanium particles colliding with the specimen substrate and the colliding scope of the effective particle depositions. The velocity and temperature distributions of the plasma flow predicted in the present study were expressed in a power form. The results predicted by the present governing equations were thus trustworthy. In general, either a small particle diameter in collaboration with a low electric potential or a large particle diameter in collaboration with a high electric potential is advantageous for a high melting and boiling points.

Abstract: Plasma spray technology utilizes the exotic properties of the plasma medium to effect physical, chemical or metallurgical reactions to produce new materials or impart new functional properties to conventional materials. It is in fact a process that includes melting, rapid solidification and quenching taking place simultaneously. As for the coating materials, it is well understood that for a number of unique application, spherical particles are preferred over irregular ones due to low surface area to volume ratio, high density, free flowing ability and close sizing etc. In view of this, the present paper reports on the preparation of glass microspheres coatings on mild steel substrate using plasma spray technology. An 80 kW atmospheric plasma spray set up is used for spraying purpose. Solid glass micro-spheres of average sized 100 micron are used as the coating materials which are deposited at four different power levels on mild steel substrate. The coatings are characterized in terms of their thickness, hardness, density and porosity. The coatability of glass micro-spheres on mild steel is assessed by evaluating the coating deposition efficiency. Different phases present in the coating are ascertained using X-ray diffractography.

Abstract: In the conventional hydroxyapatite (HAp) coating, the surface of commercially pure titanium (Cp-Ti) is blasted with Al2O3 grid-blasting powders and then plasma-sprayed with HAp. To improve the adhesive strength of HAp coating, the grid-blasting with Al2O3 powders and subsequently wet-blasting by HAp/Ti mixed powders were applied on Cp-Ti substrate at ambient temperature. On the wet-blasted surface of Cp-Ti, two-layers of coating composed of HAp/Ti bond coat and HAp top coat were deposited by plasma spraying. Both types of HAp-coated specimen could survive up to 107 cycles without spallation of HAp coating at the stress amplitude of 120 MPa under four point bending fatigue test. In order to clarify mechanical failure behavior of the coatings and Ti substrate, acoustic emission (AE) signals during the entire fatigue process were observed. Relationship between AE behavior and cracking process of coated specimen was evaluated. HAp top coat with HAp/Ti bond coat strongly improved the adhesive and cohesive strength, where dense AE signals occurred at the early stage of fatigue test corresponded to plastic deformation of Ti substrate and micro-cracks in coated layers. AE signals occurred at the final stage corresponded to crack propagation in coated specimen and spallations of coated layers.

Abstract: Plasma sprayed alumina coating is applied in many industrial applications in order to promote wear and corrosion resistance. Nonetheless, high porosity remained after deposition is a critical factor because it decreases the wear resistance. Some inorganic sealants can be used to reduce the open pores and superficial micro-cracks effect, improving the wear and corrosion resistance of alumina coatings. In this work, plasma sprayed alumina coating samples were divided into two groups: i) impregnated with inorganic sealant (AlPO4) and heat treated; ii) as deposited. Erosive wear tests were carried out in an erosion rig according to ASTM G76. The samples were subjected to an erodent flux, with impact angles of 30º up to 90º, at a velocity of 50m/s and temperatures of 25°C up to 400°C. The samples were characterized by SEM, Vickers microhardness, potentiodynamic anodic polarization and erosive wear rate. Results showed that erosive wear rate of alumina impregnated coating is lower than without the sealant. The sealed alumina coating presented higher mechanical properties; improved microstructural characteristics and the sealant promoted better lamellae contact, as can be observed by less sharpness in pits formation of microstructure.

Abstract: The modeling equations used for spallation prediction are becoming increasingly more sophisticated due to the consideration of a wider range of thermal and thermo-mechanical loading conditions. Consequently, a software application would make such life time models more practical and may become a desired tool that both academic and applied researchers may want to use. As a starting point for further development a prototype software has been developed based on a simple phenomenological spallation analysis model. This software features a Windows based graphical user interface and works with other Windows applications, such as, Power Point, Excel or Origin. The software analyzes laboratory spallation life time data acquired from isothermal, thermal cyclic and/or burner rig testing and provides confidence limits and accuracy assessment of the analysis model. It further calculates the life time for a given bond coat temperature, temperature gradient across the coating, and thermal cycle frequency.

Abstract: A zircon coating was applied on the surface of Ti-6Al-4V alloy by plasma spray and its effect on the high temperature tensile properties of the alloy as well as the oxidation behavior of the alloy were studied. Tensile tests were conducted at 850°C with different strain rates of 10-4s-1,10-3s- 1, 10-2s-1 and 10-1s-1. The results show that the elongation of the coated specimens is higher than that of the uncoated ones, while the ultimate tensile strength of the alloy is not changed. An oxide film had formed on the surface of uncoated Ti-6Al-4V alloy, however no such oxide film was found on the coated alloy at the early of stage. The coating can prevent oxygen penetration into the substrate thus prevent embrittlement of the subsurface zone. The ductility could be improved by means of the zircon coating. The optical micrographs of the specimens show little change in microstructures of the coated and uncoated specimens. Zircon coating has no effect on the microstructure of the substrate alloy.

Abstract: The protein adsorption behavior was investigated for highly (001) oriented hydroxypatatite coatings (HACs). Highly (001) oriented (HO-) HACs and HAC with low orientation (LO-HAC) were prepared on titanium (Ti) substrates through a radio-frequency thermal plasma spraying method. Sintered HA pellets (S-HA) was also prepared as a control. The solution of 22 'g/100 'l PBS of the fluorescein-isothiocyanate (FITC) labeled bovine serum albumin (FITC-BSA), immunoglobulin G (FITC-IgG) and cytochrom c (FITC-CCC) was separately dropped on the surface of HACs and was incubated for 30 min. After the incubation, such HACs were washed with the PBS additionally supplemented with 125mM NaCl and observed using a fluorescence microscope. Fluorescence microscopic examination indicates that FITC labeled proteins somewhat adsorbed on the HACs, while proteins adsorbed little on S-HA surface. In particular, it can be seen that FITC-CCC adsorbed more prominently on the HO-HAC.

Abstract: One of the most important use of thermal spray coatings is for wear resistance. In this work, the tribological properties of plasma prayed Al83.7Fe7Cr6.3Ti3 quasicrystalline coatings have been studied. The quasicrystal powders of Al-base alloys were produced by gas atomization unit in vacuum. The plasma spray process was used to produce quasicrystalline coatings. Then, friction experiments were carried out on a pin-on-disc-type tribometer. The results indicated that the friction coefficient of Al83.7Fe7Cr6.3Ti3 quasicrystalline coating is about 50% lower than that of Al70Fe13Cu10Cr7 quasicrystalline coating.